Placeholder (noun)

1. A symbol or dummy text that holds the place of something that is not yet known or has yet to be written.
2. A temporary substitute for a missing or unknown quantity, value, or person.

Origin:

Unknown origin, likely a calque (loan translation) from german platzhalter, literally 'place holder'.

Examples:

1. The author used the placeholder 'TBD' to indicate sections of the text that needed further revision.
2. The placeholder value in the computer program was used to test the algorithms before actual data was available.
3. The placeholder name was used to reserve a spot in the lineup until the real team was finalized.
4. The placeholder text was used in the design of the website to show what the content would look like.
5. The placeholder image was used to show the intended size and aspect ratio of the final graphic.